Compounds BaCe 0.7 Er 0.2 In 0.1 O 2.85 and BaCe 0.7 Er 0.2 Y 0.1 O 2.85 have been synthesized by solid state reactions. The characterization of compounds has been carried out by X-ray power diffraction. The space group and lattice parameters have been determined. Standard formation enthalpies have been measured by solution calorimetry, stabilization energies and lattice enthalpies have been calculated. It has been shown that lattice enthalpies are increased when yttrium is replaced by indium, which correlates with decreasing ionic radius from yttrium to indium.